Heterocyclic dications as a new class of telomeric G-quadruplex targeting agents

Small molecules that can induce and stabilize G-quadruplex DNA structures represent a novel approach for anti-cancer and anti-parasitic therapy and extensive efforts have been directed towards discovering lead compounds that are capable of stabilizing quadruplexes. The purpose of this study is to explore conformational modifications in a series of heterocyclic dications to discover structural motifs that can selectively bind and stabilize specific G-quadruplexes, such as those present in the human telomere. The G-quadruplex has various potential recognition sites for small molecules; however, the primary interaction site of most of these ligands is the terminal tetrads. Similar to duplex-DNA groove recognition, quadruplex groove recognition by small molecules offers the potential for enhanced selectivity that can be developed into a viable therapeutic strategy. The compounds investigated were selected based on preliminary studies with DB832, a bifuryl-phenyl diamidine with a unique telomere interaction. This compound provides a paradigm that can help in understanding the optimum compound-DNA interactions that lead to quadruplex groove recognition. DNA recognition by the DB832 derivatives was investigated by biophysical experiments such as thermal melting, circular dichroism, mass spectrometry and NMR. Biological studies were also performed to complement the biophysical data. The results suggest a complex binding mechanism which involves the recognition of grooves for some ligands as well as stacking at the terminal tetrads of the human telomeric G-quadruplex for most of the ligands. These molecules represent an excellent starting point for further SAR analysis for diverse modes of quadruplex recognition and subsequent structure optimization for drug development.     

具抑制端粒酶活性的G-四链体小分子配体研究进展

端粒酶能阻止端粒的缩短使细胞无限增殖形成肿瘤。端粒3′端富G序列在一定生理条件下可形成具有抑制端粒酶活性的G-四链体结构,从而达到促进肿瘤细胞凋亡的作用。能够诱导DNA特别是致癌基因富G区域形成并稳定G-四链体结构的配体具有重要的抗肿瘤意义。以G-四链体为抗癌药物作用靶点对化合物进行筛选和结构设计是目前化学家和生物学家的关注点。该文对近年来以G-四链体为靶点的小分子端粒酶抑制剂的研究进行了综述。     

Non-invasive erythromycin-resistant pneumococcal isolates are more often non-susceptible to more antimicrobial agents than invasive isolates

Multiresistant Streptococcus pneumoniae infections are of great concern as treatment failures may occur with commonly used treatment regimens using β-lactams and macrolides. The proportion of non-susceptible S. pneumoniae differs from country to country. In Denmark, the proportion of invasive penicillin- or erythromycin-non-susceptible isolates is still low. The aim of this study was to characterise and compare invasive and non-invasive penicillin-non-susceptible and erythromycin-resistant pneumococcal isolates from the same geographic area and the same time period with respect to serotype and antibiotic susceptibility profile. We aimed to identify which serotypes were multiresistant among Danish isolates and to confirm or reject whether there was a difference in serotype distribution and resistance profiles between invasive and non-invasive isolates. We observed that non-invasive penicillin-non-susceptible pneumococci had higher serotype diversity than invasive isolates. This was not the case for erythromycin-resistant pneumococci. The dominant serotypes among non-susceptible invasive isolates were serotypes 9V and 14, whereas the dominant serotypes among non-susceptible non-invasive isolates were serotypes 19F, 14, 9V, 6B and non-typeable (NT). Non-invasive isolates were also more likely to be resistant to three or more antimicrobial agents than invasive isolates, however isolates being multiresistant were often co-resistant to the same antimicrobial agents.     

Molecular modeling studies on G-quadruplex complexes of telomerase inhibitors: structure-activity relationships

Inhibition of the ability of the enzyme telomerase to add telomeric repeats to the end of chromosomes is a novel target for potential anticancer therapy. This paper examines the hypothesis that compounds possessing a planar aromatic chromophore inhibit telomerase via stabilization of, and binding to, a folded guanine quadruplex structure. Two series of telomerase inhibitors have been designed based on the 2,6-disubstituted amidoanthracene-9,10-dione and 3,6-disubstituted acridine chromophores in order to investigate structure-activity relationships between biological activity and substituent group size. The relative binding energies between these compounds and the folded human telomere DNA quadruplex were determined using molecular simulation methods, involving explicitly solvated structures. The results obtained are in excellent agreement with the biological activity as measured in vitro using a modified TRAP assay and in general agreement with the ranking order of binding enthalpies found in isothermal titration calorimetry studies. This broad agreement provides strong support for the hypothesis that guanine quadruplexes are the primary target for telomerase inhibitors with extended planar chromophores.     

Smartphones are more reinforcing than food for students

College students engage in high-frequency smartphone use, despite potential negative consequences. One way to conceptualize this behavior is to consider it a highly reinforcing activity. Comparing motivation for smartphones to a powerful primary reinforcer, such as food, can establish their relative reinforcing value. This study investigated whether smartphones were more reinforcing than food, as well as the relationships between smartphone reinforcement, texting use, and smartphone motives. Participants were 76 college students (50% female, M_age = 18.9, SD = 0.99) who had no access to food for three hours and to their smartphones for two hours. After this modest deprivation period, participants worked for time to use their smartphones and 100-cal portions of their favorite snack food concurrently, with the work to obtain portions of both commodities increasing. The amount of smartphone use earned during the task was manipulated across groups (20, 30, 60, 120 s) to establish what amount of smartphone use was needed to motivate responding. Additionally, reinforcing efficacy of smartphones and food using a hypothetical purchase task and motivations for smartphone use was collected. Smartphones were more reinforcing than food using either measurement methodology (p's < 0.001). Smartphone reinforcement predicted number of text messages, controlling for age, sex, and family income. Positive smartphone use motives were associated with reinforcing efficacy of smartphones. These data show that smartphones are potent reinforcers, and are more reinforcing than food given modest food deprivation. These methods provide one important reason why people may use smartphones.     

Neuroendocrine disruption: more than hormones are upset

Only a small proportion of the published research on endocrine-disrupting chemicals (EDC) directly examined effects on neuroendocrine processes. There is an expanding body of evidence that anthropogenic chemicals exert effects on neuroendocrine systems and that these changes might impact peripheral organ systems and physiological processes. Neuroendocrine disruption extends the concept of endocrine disruption to include the full breadth of integrative physiology (i.e., more than hormones are upset). Pollutants may also disrupt numerous other neurochemical pathways to affect an animal's capacity to reproduce, develop and grow, or deal with stress and other challenges. Several examples are presented in this review, from both vertebrates and invertebrates, illustrating that diverse environmental pollutants including pharmaceuticals, organochlorine pesticides, and industrial contaminants have the potential to disrupt neuroendocrine control mechanisms. While most investigations on EDC are carried out with vertebrate models, an attempt is also made to highlight the importance of research on invertebrate neuroendocrine disruption. The neurophysiology of many invertebrates is well described and many of their neurotransmitters are similar or identical to those in vertebrates; therefore, lessons learned from one group of organisms may help us understand potential adverse effects in others. This review argues for the adoption of systems biology and integrative physiology to address the effects of EDC. Effects of pulp and paper mill effluents on fish reproduction are a good example of where relatively narrow hypothesis testing strategies (e.g., whether or not pollutants are sex steroid mimics) have only partially solved a major problem in environmental biology. It is clear that a global, integrative physiological approach, including improved understanding of neuroendocrine control mechanisms, is warranted to fully understand the impacts of pulp and paper mill effluents. Neuroendocrine disruptors are defined as pollutants in the environment that are capable of acting as agonists/antagonists or modulators of the synthesis and/or metabolism of neuropeptides, neurotransmitters, or neurohormones, which subsequently alter diverse physiological, behavioral, or hormonal processes to affect an animal's capacity to reproduce, develop and grow, or deal with stress and other challenges. By adopting a definition of neuroendocrine disruption that encompasses both direct physiological targets and their indirect downstream effects, from the level of the individual to the ecosystem, a more comprehensive picture of the consequences of environmentally relevant EDC exposure may emerge.     

Quadruplex-interactive agents as telomerase inhibitors: synthesis of porphyrins and structure-activity relationship for the inhibition of telomerase.

The cationic porphyrin 5,10,15,20-tetra-(N-methyl-4-pyridyl)porphyrin (TMPyP4) binds to quadruplex DNA and is thereby an inhibitor of human telomerase (Wheelhouse et al. J. Am. Chem. Soc. 1998, 120, 3261-3262). Herein the synthesis and telomerase-inhibiting activity of a wide range of analogues of TMPyP4 are reported, from which rules for a structure-activity relationship (SAR) have been discerned: (1) stacking interactions are critical for telomerase inhibition, (2) positively charged substituents are important but may be interchanged and combined with hydrogen-bonding groups, and (3) substitution is tolerated only on the meso positions of the porphyrin ring, and the bulk of the substituents should be matched to the width of the grooves in which they putatively lie. This SAR is consistent with a model presented for the complexation of TMPyP4 with human telomeric quadruplex DNA.     

Synthesis and evaluation of quindoline derivatives as G-quadruplex inducing and stabilizing ligands and potential inhibitors of telomerase

A new series of quindoline derivatives (4a-j) were designed and synthesized to develop novel and potent telomerase inhibitors. The interaction of the G-quadruplex of human telomere DNA with these newly designed molecules was examined via circular dichroism spectroscopy and electrophoretic mobility shift assay (EMSA). The selectivity between the quindoline derivative (4a) and G-quadruplex or duplex DNA was investigated by competition dialysis. These new compounds as inhibitors of telomerase were also investigated through the utilization of modified telomerase repeat amplification protocol (TRAP) assay. The results revealed that the introduction of electron-donating groups such as substituted amino groups at the C-11 position of quindoline significantly improved the inhibitory effect on telomerase activity ((Tel)IC50 > 138 microM for quindoline, 0.44-12.3 microM for quindoline derivatives 4a-j). The quindoline derivatives not only stabilized the G-quadruplex structure but also induced the G-rich telomeric repeated DNA sequence to fold into quadruplex.     

Trisubstituted acridines as G-quadruplex telomere targeting agents. Effects of extensions of the 3,6- and 9-side chains on quadruplex binding, telomerase activity, and cell proliferation

The synthesis is reported of a group of 3,6,9-trisubstituted acridine compounds as telomeric quadruplex-stabilizing ligands with systematic variations at the 3-, 6-, and 9-positions. A new microwave-assisted methodology has been developed for trisubstituted acridine synthesis. Structure-activity relationships are reported using surface plasmon resonance and a fluorescence melting assay to examine quadruplex binding, together with a telomerase inhibition assay. These reveal relationships between G-quadruplex stabilization and telomerase inhibition and optimal 3,6- and 9-substituent side-chain lengths for maximal activity. Qualitative molecular modeling using molecular dynamics simulations has been undertaken on four quadruplex-DNA complexes. Long-term exposure of MCF7 cancer cells to a subset of the most active compounds, at doses lower than the IC(50) values, showed that one compound produced a marked decrease in population growth, accompanied by senescence, which is consistent with telomere targeting by this agent.     

Gel vehicles are not inherently more irritating than creams

BACKGROUND: It has been thought that topical gels are inherently more irritating than topical creams. Nevertheless, the irritancies of topical products are potentially quite variable, and a priori assumptions about relative irritancy of gels versus creams may not be accurate. PURPOSE: To determine whether a metronidazole gel formulation is more or less irritating to the skin compared to metronidazole creams. METHODS: A total of 32 normal, healthy volunteers were tested using irritancy patches with 0.75% metronidazole gel and cream, 1% metronidazole cream, and petrolatum (used as the "negative control"). Blinded observers evaluated the application sites for signs of irritancy. A numerical score was assigned to these irritancy patch sites each day for 21 days, or until significant irritation developed, and cumulative irritancy scores were calculated for the study period. A mixed model of variance analysis was performed. RESULTS: After 21 days of evaluation, analysis of the mean cumulative irritancy scores for each of the agents used showed there to be no statistical difference in irritancy potential between the metronidazole gel and the metronidazole creams. However, the 1% metronidazole cream was significantly more irritating than petrolatum. CONCLUSION: There was no significant difference in the cumulative irritancy potential of cream and gel preparations of metronidazole. The irritancy of topical formulations for treating rosacea should be considered on a case by case basis.